X.A.N.A. is a malevolent sentient artificial intelligence (multi-agent system) that seems to only exist to take over the world. X.A.N.A. was created by Franz Hopper. It has the ability to launch attacks by activating Towers in Lyoko, and usually employs monsters programmed by it to stop the main heroes from deactivating them, and thus, ruin its plans. It can manipulate electricity, and possess anything and anyone, putting them under its control to carry out its goals.
It is miraculously reawakened and reactivated in the fifth season, Code Lyoko Evolution. It is assumed that Professor Tyron has unknowingly resurrected the evil multi-agent system by accident.